TEC BMX NONRECEPTOR TYROSINE KINASES ARE INVOLVED IN REGULATION OF RHO AND SERUM RESPONSE FACTOR BY G-ALPHA-12/13/

A transient transfection system was used to identify regulators and ef fecters for Tec and Bmx, members of the Tec non-receptor tyrosine kina se family. We found that Tec and Bmx activate serum response factor (S RF), in synergy with constitutively active a subunits of the G12 famil y of GTP-binding proteins, in transiently transfected NIH 3T3 cells. T he SRF activation is sensitive to C3, suggesting the involvement of Rh o, The kinase and Tec homology (TH) domains of the kinases are require d for SRF activation. In addition, kinase-deficient mutants of Bmx are able to inhibit G alpha 13- and G alpha 12-induced SRF activation, an d to suppress thrombin-induced SRF activation in cells lacking G alpha q/11, where thrombin's effect is mediated by G12/13 proteins. Moreove r, expression of G alpha 12 and G alpha 13 stimulates autophosphorylat ion and transphosphorylation activities of Tec. Thus, the evidence ind icates that Tec kinases are involved in G alpha 12/13-induced, Rhomedi ated activation of SRF. Furthermore, Src, which was previously shown t o activate kinase activities of Tec kinases, activates SRF predominant ly in Rho-independent pathways in 3T3 cells, as shown by the fact that C3 did not block Src-mediated SRF activation. However, the Rho-depend ent pathway becomes significant when Tec is overexpressed.